Headbox for a paper machine, board machine, pulp machine or equivalent

Abstract

A headbox, for example, in a pulp or board machine, is suitable for high basis weights which are over 400 g / m2 and for high fiber suspension consistencies which are in a range of 2–5%. The headbox has a turbulence part (1), into which a fiber suspension flows from a tube bank (2), and a slice part (3) which is situated after the turbulence part and from which the fiber suspension flows to a forming section of a fibrous web. The turbulence part (1) of the headbox has at least two passages (5, 6), which converge in the flow direction of the fiber suspension towards the slice part (3). In that connection, the fiber suspension flow is first fluidized in a tortuous turbulence passage part (11) and, after that, it decelerates in another widening deceleration passage (12).

Description

CROSS REFERENCES TO RELATED APPLICATIONS[0001]This application is a U.S. national stage application of International Application No. PCT / FI01 / 00421, filed May 3, 2001, and claims priority on Finnish Application No. 20001067 filed May 8, 2000, the disclosures of both of which application are incorporated by reference herein.STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT[0002]Not applicationBACKGROUND OF THE INVENTION[0003]The present invention relates to paper machines, board machines, pulp machines or equivalent. More specifically, the present invention relates to a headbox [according to the preamble of claim 1, which headbox is ] suitable for high basis weights and high fibre suspension consistencies.[0004]This kind of conventional headbox of a paper machine or board machine or pulp machine or equivalent is thus, for example, of the kind comprising a turbulence part for producing a turbulent fibre suspension flow, into which turbulence ...

AI Technical Summary

Benefits of technology

[0007]It is an object of the present invention to eliminate or at least reduce the above-noted problems associated with the use of high consistency and to provide an improved headbox which is suitable for high fibre suspension consistencies which are in a range of 2–5%. The device according to the invention is particularly suitable for high basis weights of over 400 g / m2, which are used in pulp-drying machines.

[0010]In accordance with an advantageous embodiment of the invention, in the turbulence part, the angle of widening of an individual deceleration passage of the fibre suspension flow has been selected such that the suspension cannot become separated from the wall. In that connection, the angle is in a range of 0.5–7°, advantageously in a range of 2–3°, in which connection the risk of cavitation is minimized.

[0012]It is also advantageous to the invention that the height of the slice part is selected such that the flow rate of the suspension flow slowed down in the deceleration passage is maintained in the slice part in order to eliminate flocculation. In that connection, it is particularly advantageous, when the turbulence part has a double passage structure, that the cross-sectional flow area in the slice part is twice the cross-sectional flow area of a single deceleration passage, preferably at the outlet end of the deceleration passage. When the turbulence part has a triple passage construction, for maintaining the flow rate of the suspension flow and for preventing flocculation it is advantageous that the cross-sectional flow area in the slice part is three times the cross-sectional flow area of a single deceleration passage, preferably at the outlet end of the deceleration passage.

[0014]With regard to the advantages of the invention, it may be mentioned that, for example, in pulp machines, investment savings are of the order of 3.5–5.9 million euros with the current cost structure and, because of smaller flow volumes in the short circulation and in the wire section, annual pumping savings can be achieved which are of the order of 0.15–0.35 million euros with the current cost structure. A further advantage is that the capacity of old machines can be increased in connection with rebuilding.

Problems solved by technology

On the other hand, increase of fluidization limits increase of basis weight, for example, in pulp-drying machines and board machines.

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